1. Field of the Invention
The present invention relates to a heat sensitive recording material obtained by forming an intermediate layer on a heat sensitive color forming layer of a support and forming a protective layer comprising a UV-ray curable resin on the intermediate layer and, more in particular, it relates to a heat sensitive recording material of excellent light fastness capable of improving the close adhesion with the protective layer while protecting the heat sensitive color forming layer against the UV-ray curable resin constituting the protective layer and capable of preventing discoloration at the background of the support based on an oxygen-shielding property, by forming the intermediate layer with a composition containing an acrylic emulsion and a polyvinyl alcohol.
2. Description of Related Art
Heretofore, heat sensitive recording materials of utilizing colorless or pale colored color forming materials and color developing materials capable of causing the coloring forming materials to form colors upon heating have been generally known publicly and such heat sensitive recording materials can be obtained by dispersing a leuco dye and a color developing agent such as a phenolic material separately each in a finely particulate state, then mixing both of them, adding additives such as a binder, a sensitizer, a filler and a lubricant thereto to prepare a coating solution and then coating the same on a support such as paper, film or synthesis paper. While thermal printers incorporating a thermal head are used for coloring such a heat sensitive recording sheet, they are used generally in the field, for example, of facsimiles, automatic ticket machines and heat sensitive recording type labels by taking the advantageous features of causing less noises, being maintenance free, and the machines are relatively inexpensive compared with other recording methods.
Further, for providing the heat sensitive recording sheet with solvent resistance, plasticizer resistance, and water proofness, provision of a protective layer on a heat sensitive color forming layer is described, for example, in Japanese patent unexamined application publication No. 64(1989)-4387 and use of a UV-ray curable resin for forming the protective layer is described in Japanese patent examined application publication No. 58(1983)-35478.
However, the protective layer formed of the UV-curable resin has a drawback that adhesion with heat sensitive color forming layer is poor and easily defoliated by fraction or an adhesive tape. Further, for improving the light fastness, it is necessary to increase the thickness of the protective layer, which results in a problem of increase in the cost of the material for forming the protective layer or a problem of causing cracking in the protective layer.
For improving the adhesion between the heat sensitive color forming layer and the protective layer, it may be considered to provide an intermediate layer between the heat sensitive color forming layer and the protective layer. However, in a case of forming the protective layer from the UV-ray curable resin, an intermediate layer capable of simultaneously improving the adhesion with the protective layer while protecting the heat sensitive color forming layer against the UV-ray curable resin, and preventing discoloration at the background of a support to which the heat sensitive color forming layer is formed by providing the intermediate layer with oxygen shielding property has not yet been present so far.